The invention relates generally to an internal-gear machine such as an internal-gear pump.
Generally, in internal-gear machines of that kind, such as a pump, an externally toothed pinion or pump impeller is mounted eccentrically with respect to the body of the pump for actuating an internally toothed annular gear which rotates in the casing of the pump. Flow through the pump is practically continuous and without reversals and high rotary speeds may be used. In order to reduce leakage, a filling member may be disposed in the clearance between the internally and externally toothed gears, the filling member extending generally in the circumferential direction of the annular gear and being of an arcuate or sickle-shaped configuration. The filler member may be mounted movably in the casing in such a way that in operation it can follow the movements of the internally toothed annular gear and the externally toothed pinion which mesh with each other, in order thereby to compensate for radial leakage gaps which occur by virtue of the movement of those components (see German laid-open application (DE-OS) No. 15 53 027 and Swiss patent specification No. 601 670). Specific control of the hydraulic forces acting on the filling member, such control being provided by means of pilot control grooves or slots provided on the filling member and/or surfaces of the arrangement which bear thereagainst, with such grooves or slots being subjected to a preliminary filling action to provide the above-mentioned control (see the above-quoted German laid-open application) is designed to ensure that the filling member is at least partially held by the action of the hydraulic forces in the optimum position required for producing the sealing action in each situation of use, that is to say, the filling member is suitable pressed against the tips of the teeth of the internally toothed annular gear and the externally toothed pinion. By virtue of the above-indicated control configuration, the direction and the magnitude of the forces involved is determined by the level of the operating pressure obtaining in the pressure chamber defined between the pinion and the annular gear, and the configuration of the separating surface, which is governed by the control requirement, between the intake chamber and the pressure chamber defined within the casing between the annular gear and the pinion. However, strictly speaking, those forces are unambiguously defined only when the machine is operating in a steady state. In contrast, if there is no operating pressure obtaining in the pressure chamber of the machine or if the machine is operating in a condition in which the pressure in the intake chamber thereof even exceeds the pressure in the pressure chamber, which may be the case when using filling pumps which are connected at an upstream location, then the filling member is subjected to the effect of forces which urge it towards the location at which the teeth of the pinion and the annular gear come into mesh with each other. In that situation, in conjunction with the frictional forces between the filling member and the tips of the teeth of the pinion and the annular gear, which forces act in any case on the filling member in the above-indicated direction, there is the risk that the filling member may be entrained by the movement of the pinion and the annular gear and may then become wedged and jammed between them at the location at which they come into meshing engagement with each other. That results in immediate seizure of the machine, with adverse consequences on the items of equipment connected thereto.
In order to reduce the risk of such a jamming effect, the filling member may be mounted in the casing, in the clearance between the externally toothed pinion and the internally toothed annular gear, in such a way that it is rotatable and slidable in the casing. That form of mounting can be achieved by means of a mounting pin which is carried rotatably in a bore in the casing, and a mounting portion which is displaceable in a groove. In that way, the filling member is held securely in both circumferential directions in the casing, without thereby adversely affecting the freedom of movement for the purposes of compensating for the radial clearance. However that kind of construction suffers from the disadvantage that the mounting pin which passes through the filling member is of restricted diameter, having regard to the dimensions of the filling member, and therefore is not capable of withstanding high operating pressures. Therefore, in order to be able to use higher operating pressures with that arrangement, the design configuration has been amended to provide for mounting pins for the filling member, which extend entirely outside the filling member, which have a support surface for the filling member and which for that reason can be of a stronger construction. However, in order to avoid the above-mentioned jamming effect in that construction, the arrangement also included a spring pin for the purposes of retaining the filling member in position, as disclosed for example in German laid-open application (DE-OS) No 23 12 085. However, in the above-mentioned operating condition in which the pressure in the intake chamber is the predominant pressure in the arrangement, the spring pin is not always capable of reliably preventing the filling member from being drawn into the location of meshing engagement between the teeth of the pinion and the annular gear when the machine is running. That also applies to an increased extent in situations in which the material being conveyed for example by the pump is of very low viscosity and possibly may also not have any kind of lubricating action.
It will be appreciated that, when dealing with materials of that kind, which are of low viscosity, in order to provide an adequate sealing effect it is necessary for the filling member to be longer than when the machine is designed for dealing with material to be conveyed which is of higher viscosity. However the increased length of filling member results in the filling member being in simultaneous engagement with the tips of a larger number of teeth in the assembly, which in turn results in a higher level of frictional force seeking to pull the filling member into the location of meshing engagement between the teeth of the annular gear and the pinion.